The long-term objective of this study is to reduce risk for HIV and other sexually transmitted diseases (STDs) during and after pregnancy among ethnically-diverse adolescents (aged 14-19) receiving prenatal care in public clinics in 2 cities: New Haven CT and Atlanta GA. Because women of all ages make numerous behavioral changes during pregnancy (e.g., improve diet; reduce/eliminate tobacco, alcohol and illicit drug use), we believe that pregnancy may also present an important window of opportunity to promote changes in high-risk sexual behavior. Behavior changes initiated in pregnancy could be maintained postpartum with an effective intervention. Integrating theories of diffusion of innovation, social learning theory, and theory of gender and power, specific aims of the proposed study are to: (1) Implement a unique group prenatal care intervention that focuses on risk assessment, educational/skills development, and social support to reduce health risk behaviors and promote health enhancing behaviors; (2) examine prospectively changes in behavior throughout the prenatal period and up to one year later, and to determine the effects of these behavioral changes on biological outcomes, including incidence of STDs and repeat pregnancy; and (3) Identify HIV risk-related psychosocial characteristics associated with biological and behavioral outcomes. As part of this randomized controlled trial, women entering prenatal care in the collaborating clinics will be randomly assigned to one of three treatment conditions: individual standard of prenatal care, standard Centering Pregnancy Program for group prenatal care, and enhanced Centering Pregnancy Program including HIV/STD skills development. The principal outcome will be subsequent chlamydial or gonorrheal infection, evaluated on an intent-to-treat basis by logistic regression analysis. The strengths of the proposed study include: its randomized, prospective longitudinal design; opportunity to maximize sexual risk reduction during and after teen pregnancy; integration of biological and behavioral outcomes; intervention implemented in two cities with high HIV/STD prevalence; change social norms regarding high-risk behavior during pregnancy/postpartum by conducting prenatal care in peer groups; and ability to sustain the intervention because prenatal care is covered by most standard reimbursement systems -- both public and private (i.e. ease of technology transfer).